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4 air exchanges per hour: A history of calf barn ventilation and an industry that is slow to change

Ryan Leiterman for Progressive Dairy Published on 31 March 2021

When discussing calf barn ventilation, invariably the topic of using four air exchanges per hour for cold-weather ventilation will come up. After all, we wouldn’t want “too much” of that cold air in the barn. Or would we?

Who came up with the idea to use four air exchanges per hour during cold weather and why? To understand our industry’s current ventilation recommendations, we must first understand the history of calf barn ventilation research.

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Over the winter of 1977, the University of Minnesota conducted a research trial evaluating calf respiratory health by comparing two different ventilation rates: one air exchange per hour versus four air exchanges per hour. One group of 40 Holstein bull calves received a ventilation rate of one air exchange per hour, while another group of 40 Holstein bull calves received a ventilation rate of four air exchanges per hour.

All other variables were kept constant between the groups of calves. At the end of the trial, calves from each group were euthanized and their lungs were examined. The study concluded that the calves raised with four air exchanges per hour had fewer cases of pneumonia when compared to calves raised with one air exchange per hour.

In 1979, Dr. Bates, a professor at the University of Minnesota, published the 1977 trial results in a paper titled “Calculation of ventilation needs for confined cattle,” in which he stated, “For air purity, the fundamental criterion in designing a calf barn ventilation system is to provide continuous exhaust at a minimal rate of about four air changes per hour. This will reduce aerosol contaminates in addition to controlling moisture.”

Note that Dr. Bates refers to four air changes per hour as a minimal air exchange rate, suggesting that higher ventilation rates may be necessary.

Nearly every scholarly publication regarding calf barn ventilation in the past 20 years recommends four air changes per hour during cold weather, citing the paper of Dr. Bates in 1979 (see Figure 1).

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History of four air changes

To date, peer-reviewed research exploring cold-weather ventilation rates greater than four air changes per hour has not been conducted.

In 2002, Dr. Bradford Smith released the third edition of Large Animal Internal Medicine, where he states that mechanically ventilated barns should have a “fan capacity to achieve four air changes per hour in winter” and provides the paper written by Bates in 1979 as the citation for that recommendation.

In 2006, Dr. Lago published a paper titled: “Calf respiratory disease and pen microenvironments in naturally ventilated calf barns in winter,” where he discussed the differing recommendations for minimal ventilation rates of calf barns and cites the 1979 paper of Dr. Bates.

In 2007, Dr. Ken Nordlund published a paper titled: “Housing factors to optimize respiratory health of calves in naturally ventilated calf barns in winter,” where he cites the 1979 work of Dr. Bates stating that cold-weather ventilation systems should be used to “direct small volumes of fresh air into the pens.”

In 2008, Dr. Ken Nordlund published a paper titled: “Practical considerations for ventilating calf barns in winter,” where he cites the 1979 work of Dr. Bates, stating, “Current recommendations for minimal winter ventilation rate in calf barns range from 15 cubic feet per minute to four air changes of the building per hour.”

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In 2011, Ingrid Lorenz cites the 1979 work of Dr. Bates in a paper titled “Calf health from birth to weaning III. Housing and management of calf pneumonia,” where she states: “To prevent adverse conditions, at least four air changes per hour are needed in winter.”

Why is the dairy industry still using calf barn ventilation recommendations based on a single research trial done in 1977?

The simple answer is: Change happens slowly. The real reason for a lack of change has more to do with human nature than it does with ventilation technology. A population of people is comprised of five distinct groups, and an idea or innovation must be widely adopted over time in order to self-sustain. The groups are:

1. Innovators: They are the visionaries and inventors who develop new ideas.

2. Early adopters: These people are the first to try new ideas. They jump at new products, embrace change and love being the first in their social group to do something new.

3. Early majority: They are the people who don’t want to try something until their neighbours have tried it first.

4. Late majority: These people don’t want to try something new until after most people are already doing it. They want to be sure it is a good idea. They do not love change but are willing to adapt.

5. Laggards: They are resistant or refuse to change.

Once an idea reaches acceptance from the early majority group, it acts like a tipping point and the late majority and laggards will soon follow, and the idea or innovation is widely accepted. For change to happen, a new idea must go through the same process of acceptance throughout the population in order to replace the old idea. The idea of using four air exchanges per hour for winter ventilation has been the standard in the dairy industry for a long time. When it first came out, Bates was the innovator, and he faced challenges in getting his idea to take hold. Now the idea has gone through the various stages of acceptance and has become widely adopted.

What’s next?

Before the dairy industry can advance the topic of calf barn ventilation, we must first realize that the recommendation of Bates in his 1979 paper was: Four air exchanges per hour in the winter should be viewed as a minimum ventilation rate.

There is a common belief in the dairy industry that if we bring in “too much” fresh air into the barn it will create a draft on the calves – but this is not true. Using modern ventilation methods, it’s quite easy to achieve higher ventilation rates without causing a draft. Furthermore, calves raised outdoors in hutches have significantly lower respiratory disease rates than their barn-raised counterparts, showing us that in the absence of a draft, there is no such thing as “too much” fresh air.

Four air exchanges per hour has been proven to be better for calf health than one air exchange per hour. So shouldn’t we as an industry be curious if six, eight or maybe even 10 air exchanges per hour would be better than four? Some of the innovators and early adopters in our industry are already using winter ventilation rates greater than four air exchanges per hour and seeing positive results.

Our industry needs new, innovative research that compares air quality and calf health with cold-weather ventilation rates greater than four air changes per hour.

Numerous improvements in calf housing and welfare have been made over the last four decades, but our industry still suffers from too much calfhood pneumonia. Until the day comes that calves in barns have the same or less respiratory disease as calves housed in outdoor hutches, the work on improving calf barn ventilation is not finished.

The first step to change is innovation, and innovation can only be driven by curiosity. We as an industry need to be curious and start to wonder if four air changes per hour is the best option for our calves. New and updated research is needed.  end mark

References omitted but are available upon request. Click here to email an editor.

Ryan Leiterman
  • Ryan Leiterman

  • Director of Technical Services
  • Crystal Creek Natural LLC
  • Email Ryan Leiterman

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